Laser devices emitting infrared light are applied to a broad range of fields such as environment measurement. A quantum cascade laser made of a semiconductor is small in size and has high convenience, and enables high precision measurement.
The quantum cascade laser includes an active layer alternately stacked with, for example, GaInAs and AlInAs, and including a quantum well layer. The quantum cascade laser has a structure where both side surfaces of the active layer are interposed between, for example, InP cladding layers. In this case, the cascade-connected quantum well layer is capable of emitting infrared laser light with a wavelength of 4 to 20 μm by intersubband transition of a carrier.
Various gases included in air have an absorption spectrum peculiar to the gas due to infrared ray radiation. For this reason, type and concentration of the gas can be known by measuring an infrared ray absorption amount. In this case, a wavelength range of the laser light emitted from the quantum cascade laser is required to be wide.